Presently, the desire for antennas for transmitting radio frequency signals from a small, compact location to an external receiver has grown significantly. For example, antennas for transmitting radio frequency signals from a recording or monitoring device, such as a thermostat, water meter, gas meter, electric meter or any similar type of device to a remote location that is configured to monitor and record the status of the device have become increasingly desirable. Since many of the devices utilizing an RF antenna are produced in very large quantities, a desire and need exists for an antenna that can transmit the RF signals a desired distance while being low in cost to produce and assemble.
Typically, an antenna structure is formed separate from the printed circuit board that includes the antenna driving circuit. The separate antenna device increases the cost to produce the combination of the antenna and driving circuit while also increasing the size of the compartment needed to house the two separate components.
In an effort to avoid the use of external antennas, manufacturers have utilized micro strip patch antennas, the characteristics of which are well known. Briefly, a micro strip patch antenna includes a dielectric material, such as a printed circuit board, which has two opposed surfaces. One of the surfaces is coated with an electrically conductive layer that functions as a ground plane and the opposed surface has an essentially rectangular or circular shaped electrically conductive layer (micro strip patch) disposed to extend over the ground plane. The micro strip patch antenna presents a thin resonating cavity where standing electromagnetic waves can exist and can be radiated from the edges of the antenna.
Micro strip patch antennas, however, have many limitations, including the ability to radiate only above the ground plane. Further, because the micro strip patch antenna has a resonant cavity that greatly depends upon the thickness of the dielectric material utilized, tuning such an antenna is difficult. Thus, the printed circuit board forms a important part of the antenna structure, even though a PCB is typically formulated with rather low tolerances.
Therefore, it is an object of the present invention to provide a printed antenna that can be formed directly on a dielectric material, such as a printed circuit board, that also is used to mount the antenna driving circuitry. Further, the present invention seeks to provide a printed circuit antenna that functions as a dipole antenna having a radiating portion significantly less than one-half the wave length of the received/transmitted frequency range. The antenna also provides an impedance matching strip that allow the antenna to match the impedance of the antenna driving circuit by increasing or decreasing the length and configuration of the impedance matching strip.